The invention relates to a multi-sprocket arrangement which is provided for installation on a rear wheel axle of a bicycle and which has a holding body and a sprocket assembly. The sprocket assembly is composed of at least a first sprocket, which is fixed radially and axially to the holding body, and a second, self-supporting sprocket. The second sprocket is connected to the holding body via the first sprocket by way of at least one separate, cylindrical fastener which extends parallel to the rear wheel axle. The fastener has a first and a second end which are connected in frictionally fit fashion to drilled holes in the first and second sprockets. The frictionally fit connection between the fastener and the drilled holes or the sprockets prevent the first and second sprockets from moving toward one another in an axial direction.
Multi-sprocket arrangements for bicycle gearshift arrangements on rear wheel axles are normally mounted rotatably on the rear wheel axle by way of a driver with freewheel mechanism. The driver engages with the rear wheel axle via a freewheel clutch and permits a transmission of torque in the direction of rotation or drive direction and permits freewheeling, without transmission of torque, in the reverse direction of rotation. To optimize the selection of the transmission ratio, the number of sprockets is ever-increasing in modern bicycle gearshift arrangements. In particular, the use of very small sprockets with ten or even fewer teeth, and correspondingly small sprocket outer and sprocket inner diameters, is playing an ever greater role. The sprocket inner diameters are in some cases smaller than the outer diameter of the driver or of the holding body, such that said sprockets can no longer be pushed onto and fastened to said driver or holding body. Very small sprockets require alternative and space-saving fitting, for example laterally adjacent to the driver. This alternative fitting of the self-supporting sprocket however also gives rise to disadvantages. Furthermore, with the increasing number of sprockets, both the weight and the manufacturing costs of the assembly increase. There are various approaches in the prior art for attempting to overcome said disadvantages.
In order to save manufacturing costs despite the large number of sprockets, one approach is for the sprockets to be manufactured individually and connected by way of separate fasteners. In particular, the punching of individual sprockets is an inexpensive option. By contrast to an integrally formed multi-sprocket arrangement formed from a blank by turning and milling operations, said punched and subsequently connected individual sprockets are inexpensive and quick to manufacture.
A cassette of said type manufactured from individual sprockets and connected by way of simple pins is known from DE 10 2014 010 700 A1. The supporting structure of the sprocket arrangement yields, overall, a hollow body in the form of a cone. The entire cone hollow body is in contact with the driver only at two axially mutually spaced-apart positions, and is supported radially there. At said two positions, the two supporting sprockets are normally also fixed in an axial direction. The conical shape of the hollow body arises because the individual sprockets (aside from the two supporting sprockets) do not extend as far as the driver. This construction saves material and weight. Adjacent individual sprockets are connected to one another in frictionally fit fashion by way of pins that are pressed into drilled holes in the sprockets.
DE 10 2010 027 228 A1 likewise presents bolts which connect the first and second sprockets to one another in frictionally fit fashion. It is also described that an abutment collar can function as a spacer between adjacent sprockets. During the installation process, the bolts are, in a first step, pressed by way of the first end thereof into the receiving openings of a first sprocket. In a second installation step, the adjacent second sprocket is then pressed onto the second end, which remains free, of the bolt. The pressing action gives rise to a form fit between the bolt and the sprockets. Furthermore, during the pressing of the pins into a hole arrangement, it is possible for an encircling bead of low height to be formed, the action of which is similar to that of an abutment collar.
It has however been found that, in the presence of cyclic bending caused by the circulating circumferential load of the chain on the sprockets, the above-discussed frictional fit between pin/bolt and sprocket is not sufficient to ensure a secure connection. In particular, the self-supporting sprockets, which axially are not fixed in both directions or are not arranged and braced between the axially fixed sprockets (supporting sprockets), are at risk of moving apart or even becoming detached under load. A secure connection of the multi-sprocket arrangement is put at risk.
A purely form-fitting connection of adjacent sprockets by way of bolts which are deformed at the ends, together with spacers, is known from DE 10 2007 010 456 A1. The spacers are intended to facilitate the installation process. They are furthermore required because the form-fitting connection of the sprockets duly accommodates axial forces which move the sprockets apart from one another but not axial forces which move the sprockets toward one another. To also accommodate these axial forces, a spacer must be fitted between adjacent sprockets. Said further component entails costs, weight and additional installation outlay.
Furthermore, it remains to be stated that the structural space between rear wheel hub and bicycle frame is predefined. That is to say, the increasing number of sprockets must be accommodated in the same structural space. This demands a space-saving arrangement in an axial direction.